Characterization of pulsed discharge plasma at atmospheric pressure

The production of hydrogen and carbon nanotubes (CNTs) by the decomposition of methane inside the reactor using pulsed discharge plasma under conditions of room temperature and atmospheric pressure was investigated and characterized. The development of dissociation of methane with corona discharge under several conditions had been observed. We have noticed that the key radicals such as CH₃ and H produced by pulse corona plasma from source gas, will undergo chain reaction leading to efficient formation of hydrogen gas as well. We have found the external diameter and resistivity of CNTs around 50 nm and 0.15 Ω cm respectively. The main results obtained from the present experiments could be quite useful for the production of hydrogen, CNTs, and future industrial applications.     

Thin film deposition and surface modification with atmospheric pressure dielectric barrier discharges

This paper focuses on some of the most debated issues concerning the utilization of atmospheric pressure dielectric barrier discharges (DBDs) in surface processing of materials such as, for instance, the existence of different discharge regimes (filamentary and homogeneous) and the influence on the discharge behaviour of feed gas additives and substrate properties (chemical composition, electrical characteristics, etc.). Crucial aspects of the DBD operation which highly differentiate this approach from the well established low pressure plasma technology will be discussed.An overview of the state of the art in atmospheric pressure thin film deposition from fluorocarbon- or organosilicon-containing DBDs will be also provided. In particular the possibility of tailoring the chemical composition of the coatings, the etching-deposition competition and the influence of feed gas contaminants (i.e. air and H₂O) in the deposition of fluoropolymers will be discussed. Recent results on the deposition of SiO_xC_yH_z thin films from three different methyldisiloxanes (i.e. hexamethyldisiloxane, pentamethyldisiloxane and tetramethyldisiloxane) will allow to highlight the effect of the chemical structure of the organosilicon precursor and of the oxygen-to-methyldisiloxane feed ratio on the properties of the deposits. The results obtained through different diagnostic techniques of the plasma phase (i.e. optical emission spectroscopy and GC-MS analysis of the exhaust gas) and of the deposits (i.e. XPS, FT-IR, SEM, and WCA) allow to highlight interesting aspects of the fluorocarbon and organosilicon plasma chemistry at atmospheric pressure.     

Surface modification of polyester film by glow discharge tunnel at atmospheric pressure

A large-area improved dielectric barrier glow discharge tunnel has been developed for modifying the surface of polyester film at atmospheric pressure with argon and oxygen gas mixtures. The electrical properties of the glow discharge tunnel were studied by simultaneous measurement of the voltage and current. In addition, the effect of the glow discharge tunnel treatment on the surface of polyester film were studied. The resultant modifications of the surface properties of the treated samples were investigated through scanning probe microscopy and contact angle measurement.     

Influence of gas flow on argon microwave plasma jet at atmospheric pressure

Many kinds of an atmospheric-pressure plasma jet have been developed and used for widespread applications such as a surface treatment and modified. This study focused on the argon atmospheric-pressure microplasma jet generated by discharging of RF power of 2.45 GHz microwave. The plasma jet shows sensitivity to surrounding environment: pressure, temperature and gaseous species. It is therefore absolutely imperative that a nature of atmospheric-pressure plasma jet should be understood from a point of fluid dynamics. This study, therefore, focused on the interrelationship between the plasma jet and the working gas. Motion of the plasma jet and the working gas was evaluated by velocity measurement and fast photography. As a result, the unsteady sinusoidal waving motion in the radial direction of a torch was observed. Advection velocity of the plasma in just downstream region of the torch exit increases with the supplying flow rate, and the velocity ratio is in the range of 0.75-0.87.     

Surface modification of a polyester non-woven with a dielectric barrier discharge in air at medium pressure

In this paper, a polyester non-woven is plasma treated with a dielectric barrier discharge (DBD) in air at medium pressure (5.0 kPa) and at different discharge powers. Results show that an increasing power leads to a better plasma treatment of the sample. The barrier discharge is characterized by a voltage and current waveform, by a Lissajous figure and by Lichtenberg figures. The surface properties of the plasma treated samples are examined using X-ray photoelectron microscopy (XPS) and scanning electron microscopy (SEM). XPS analysis reveals that surface oxidation by the formation of oxygen-containing functional groups enhances the surface wettability. SEM analysis shows that the sample is not etched by the used barrier discharge. This is due to the low surface energy density of the DBD used in this paper. Therefore, a DBD in air at medium pressure provides an efficient modification of the chemical surface properties of textiles without destroying the physical structure.     

The use of the orthogonal array with grey relational analysis to optimize the electrical discharge machining process with multiple performance characteristics

In this paper a new approach for the optimization of the electrical discharge machining (EDM) process with multiple performance characteristics based on the orthogonal array with the grey relational analysis has been studied. A grey relational grade obtained from the grey relational analysis is used to solve the EDM process with the multiple performance characteristics. Optimal machining parameters can then be determined by the grey relational grade as the performance index. In this study, the machining parameters, namely workpiece polarity, pulse on time, duty factor, open discharge voltage, discharge current, and dielectric fluid are optimized with considerations of multiple performance characteristics including material removal rate, surface roughness, and electrode wear ratio. Experimental results have shown that machining performance in the EDM process can be improved effectively through this approach.     

The effect of an atmospheric pressure plasma treated MgO layer on the discharge performance of an AC plasma display panel

The effect of an atmospheric pressure plasma treated MgO layer on the discharge performance of an alternating current plasma display panel (AC PDP) was investigated by measuring the contact angle, the surface roughness, the composition, the breakdown and sustaining voltages. The plasma cleaning was performed using the He/O₂/Ar gas mixture. Higher contact angle (35°) of water droplet on the MgO surface and the MgO surface roughness (90 nm, R_max) after one day duration in the air was significantly reduced to 4° and 54 nm (R_max) after the plasma cleaning. After the plasma treatment, the adsorbed CO₂, CO, H₂O impurities on the MgO surface are effectively removed. The breakdown and sustaining voltages were reduced probably due to the increase of secondary electron emission coefficient of MgO, implying that the plasma cleaning process of the MgO layer is beneficial for the improvement of the discharge performance of the AC PDPs.     

Deposition and etching of fluorocarbon thin films in atmospheric pressure DBDs fed with Ar-CF4-H2 and Ar-CF4-O2 mixtures

The deposition and etching of plasma-polymerized fluorocarbon thin films were studied in filamentary dielectric barrier discharges (FDBDs) fed with Ar-CF₄-H₂ and Ar-CF₄-O₂ mixtures, respectively. The etching/polymerization competition was investigated as a function of the feed composition.Hydrogen addition to CF₄ promotes thin films deposition, with a maximum deposition rate at 20% H₂, and reduces the F/C ratio of the deposit, while the oxygen addition promotes the etching of the plasma-deposited film. It is demonstrated that fluorine atoms can perform the etching of the fluoropolymer also without ion bombardment. The correlation between the trend of the etch rate and the trend of the surface chemical composition of fluoropolymers etched in Ar-CF₄-O₂ mixtures allows to enhance hypotheses on the reaction mechanism and on the role of the different active species involved in plasma-surface interactions.     

Study of the ageing behaviour of polymer films treated with a dielectric barrier discharge in air, helium and argon at medium pressure

Plasma treatment of polymers is gaining more and more popularity as a surface modification technique, since it offers numerous advantages over the conventional chemical processes. Plasma surface treatment is an environmentally benign, fast and versatile technology. However, it has one major disadvantage: the induced modification of the surface is not permanent, since the surface tends to recover to the untreated state. This ageing effect is due to the reorientation of induced polar chemical groups into the bulk of the material. In this paper, the ageing of polypropylene (PP) and polyethylene terephthalate (PET) films, treated with a dielectric barrier discharge operating at medium pressure (5.0 kPa) in air, helium and argon, is studied. This study is performed using contact angle measurements and X-ray photoelectron spectroscopy (XPS). Results show that the working gas used during plasma treatment has a significant influence on the ageing behaviour of both PP and PET films. The air-, helium- and argon-plasma treated PP films have a loss in treatment efficiency of 47%, 35% and 25% respectively, while the air-, helium- and argon-plasma treated PET films have a loss in treatment efficiency of 39%, 34% and 29% respectively. These results can be explained by the different cross-linking degrees of the polymer films after plasma treatment. Increasing the cross-linking degree will hinder the movement of the polymer chains and reduce the ageing effect.     

Evaluation of surface and bonding properties of cold rolled steel sheet pretreated by Ar/O2 atmospheric pressure plasma at room temperature

In this study, cold rolled steel sheet for automotive was pretreated by the Ar/O₂ atmospheric pressure plasma at room temperature to improve the adhesive bonding properties. Through the analysis of contact angle and calculation of work of adhesion, the change of surface properties related to the plasma power, treatment time, and flow rate of O₂ gas were investigated before and after plasma treatment. Contact angle was degreased and work of adhesion was increased after plasma treatment. Meanwhile, the changes of surface roughness and morphology were observed by atomic force microscopy (AFM). And the chemical compositions of the steel sheet before and after plasma treatment were characterized by X-ray photoelectron spectroscopy (XPS). Surface roughness was slightly changed and new functional group, oxides, appeared on the surface of steel sheet after plasma treatment. Based on design of experiments and artificial neural network (ANN), the single lap shear test was performed to analyze the effect of plasma treatment parameters gas on adhesive bonding strength. From the result of the single lap shear test, the adhesive bonding strength of joint which was treated by Ar/O₂ atmospheric pressure plasma was improved about 23% compared with that of untreated sheet.     

The formation of diamond-like carbon film at atmospheric pressure by the pulsed laser/plasma hybrid deposition method

A pulsed laser/plasma hybrid deposition method has been developed to produce the diamond-like carbon (DLC) film at atmospheric pressure in this work. A plasma torch was used to heat up the carbon particles which were simultaneously ablated by a pulsed laser, thus the kinetic energy of the carbon particle can be increased to form the carbon atoms with amorphous bonding structure of the DLC film by this proposed hybrid deposition method.The influences of the plasma flow have been examined numerically and experimentally. In the numerical analysis, the temperatures of the plasma flow at various inlet pressures and electrode currents have been predicted. According to the experimental results of the carbon film inspected by the Raman spectroscopy, it reveals that the intensity ratio of the D-band to G-band of the carbon film can be reduced to 0.5 by the implementation of plasma flow. Therefore the DLC film was solidly formed. The adhesive strength of the DLC film was also characterized by the scratch test, it can be found that the critical loading of the film is up to 19 N.